This invention relates to an exposure controller for a camera capable of obtaining a special picture effect by changing an opening area of a diaphragm while a film is being exposed, i.e., a shutter is open.
Generally, a camera is provided with a diaphragm for restricting the amount of light reaching a film after passing a lens optical system and a shutter for causing the film to be exposed by opening for a set exposure time in order to properly expose the film. The opening area of the diaphragm and the shutter speed are factors largely influencing how pictures will turn out and are closely related to an occurrence of blurredness and a camera shake.
A lens shutter is a shutter which is provided in the lens optical system and in which the same blades are generally used as aperture blades and shutter blades, i.e., acts as a diaphragm and as a shutter. Thus, the opening area and the shutter speed cannot be set independently of each other. Therefore, the opening area and the shutter speed are determined based on a light measurement value according to the specification of the camera.
On the other hand, in a single-lens reflex camera in which a lens is exchangeable, the diaphragm and the shutter are generally separate elements, and a focal plane shutter is provided as a shutter immediately before a film. In such a single-lens reflex camera, the opening area of the diaphragm and the shutter speed are manually or automatically set such that the film is suitably exposed according to the brightness of an object. During the photographing, the diaphragm is actuated to a specified aperture value and then the shutter is actuated with the opening area fixed.
For example, Japanese Unexamined Patent Publication No. 1-316726 discloses a camera system which includes a lens shutter and a focal plane shutter, and has a lens shutter mode for actuating the lens shutter as a program shutter and a focal plane shutter mode for controlling the aperture by the lens shutter and controlling the exposure time by the focal plane shutter.
According to this camera system, the aperture value changes over time in the case that a program exposure is made by the lens shutter. Thus, a moving direction of a moving body is recognizable based on the blurredness of an image resulting from an aperture effect.
There is also a commercially available camera which can obtain an effect approximate to an effect obtained when an apodization filter is used by actuating the lens shutter in accordance with a triangular exposure curve for opening the lens shutter at a relatively low speed and closing it at a high speed (hereinafter, "apodization effect") (see pp. 66 to 71, May, 1971 issue of "Shashin Kogyo (Photographic Industry)" published by the Photographic Industry Publishing Company). The apodization filter is constructed such that transmittance is reduced along a direction perpendicular to an optical axis away from the center of the optical axis. If a picture is taken using this apodization filter, there can be obtained an effect that an out-of-focus image is made softly blurry as a whole, thereby being turned into an image which renders a satisfactory blurry effect.
However, the apodization effect cannot be obtained in the conventional single-lens reflex camera since the aperture value is held at a specified value without being changed during the exposure.
Further, in the camera system disclosed in Japanese Unexamined Patent Publication 1-316726 and the camera which operates in accordance with the triangular exposure curve, a sufficient apodization effect or a desired apodization effect suited to a photographer's purpose cannot be obtained since the lens shutter opens at a specified speed as time elapses.